Navigation is Key to AUV Missions - Paroscientific, Inc.

increased, and thus survey productivity
- an AUV should be able to
operate at four knots compared with
the present 1-2 knots of a survey
vessel with deeptow fish trailing
behind.
Various studies have been made to
calculate the savings that could be
made by using AUVs for deepwater
surveys rather than conventional
methods. Shell, for example, calculated
that over five years it could
save $100 million in terms of direct
operational costs and by reducing
design conservatism.
Since then, others have looked at
the Shell figures and extrapolated on
them. Kongsberg Simrad is one of
them: it says that overall savings on
deepwater developments worldwide
could amount to $772 million over
five years!
The Vehicles
Given this delightful prospect of
better data combined with cost savings,
it is not surprising that AUVs are
now making their appearance in the
commercial survey market. Currently
there are four main contenders:
• C&C Technologies, Lafayette,
Louisiana, has conducted deepwater
missions on BP’s Gulf of Mexico Mad
Dog and Holstein fields using its
Hugin AUV, designed and built by
Kongsberg Simrad, Norway. It is rated
to 3,000 meters, powered by a unique
aluminium oxygen fuel cell for 40-
hour endurance and has a Simrad
EM2000 multibeam sounder,
EdgeTech chirp sidescan and sub-bottom
profiler, Seabird CTD and a magnetometer.
On extended missions, the
performance of internal control systems
(including navigation) was
“exceptional,” reports BP.
• Bluefin Robotics, USA is about to
deliver the first of two Oracle vehicles
for Thales Survey, U.K., which will
have a depth capability of 3,000
meters.
• Maridan A/S, Denmark, delivered
the first M600 AUV to De Beers
Marine, Cape Town to search for diamonds
using a survey sensor payload
which includes RESON 8125 imaging
sonar, Klein 2000 digital sidescan,
GeoAoustics Geochirp sub-bottom
profiler and SRD autonomous visualisation
system. A further M600 is conducting
surveys for BP in the Gulf of
Mexico; another is working for
BP/Shell in the mid-North Sea, operating
with Gardline Surveys on a combine
geophysical-geotechnical survey.
• A potent teaming is that of Boeing
Company, Fugro GeoServices Inc and
Oceaneering International Inc. by the
end of this year they will have in the
water a 5.7 meter long vehicle that
weighs 5,300 kilograms in air, has a
10-ton handling system, 3,000 meter
depth rating and is fitted with sidescan
sonar, sub-bottom profiler, multibeam
sounder and TV.
Boeing brings its 30 years of experience
in developing and operating vehicles
for the government [it is currently
the prime contractor for the U.S.
Navy’s Long-term Mine Reconnaissance
System (LMRS)]; Fugro will
provide the sensor payload and data
analysis technologies; Oceaneering
will be responsible for surface ship
handling and the vehicle launch and
recovery system.
Navigation Systems
It’s fairly obvious that one of the key
requirements for an AUV is its navigation
system: if you are going to let
your multi-million-dollar baby go
roaming round the deep ocean unsupervised
for two days at a time you
need to be sure that she will pop up to
greet you at a pre-arranged location,
having gathered high quality data
accurately referenced to her pre-programmed
route.
So, it’s in underwater navigation
that some of the greatest innovations
are to be found in the current AUV
front-runners.
C&C’s Hugin is positioned by a
Kalman filter-aided INS system which
integrates inertial navigation with RD
Instruments’ doppler velocity log,
fiber optic gyro, depth sensor, altitude/forward-looking
sensor and
Kongsberg Simrad super short baseline
(SSBL) HiPap positioning.
Maridan reports that “underwater
navigational technology is a primary
focal point” for its engineering team.
For its AUVs, Maridan developed the
Marpos system in association with the
Danish Technical University and
Kearfott Guidance and Navigation
Corporation, USA.
Marpos is an integrated dopplerinertial
system at the core of which is
a high precision ring-laser-gyro strapdown
inertial navigation system
(INS)—the KN5053—developed by
Kearfott. The INS is mechanically
aligned with RDI’s 1200 kilohertz
DVL - which measures vehicle speed
over the ground or through water -
and, for surface navigation, a DGPS
receiver. A Kalman filter resident in
the INS performs real-time integration
of the sensor measurements to provide
accurate position, attitude and attitude
rate information in all axes.
Orientation (including heading) is
determined by Marpos in an alignment
process where the Kalman filter uses
the gyros and accelerometers to determine
local gravity vector and the
Earth’s rotation. Alignment is performed
either statically or moving
(using DGPS or RDI’s DVL) to an
accuracy of around 0.03° rms.
Marpos calculates relative position
from start-point by dead reckoning.
Sea tests with Maridan M600 have
delivered a positioning accuracy of
around 0.03 percent of total distance
traveled—the equivalent of 1.7 meters
per hour at a vehicle speed of three
knots.
Marpos can accurately determine
absolute position of start-point on the